The life and operation of certain products, such as chemical, biological, electrical, and electronic products, is often dependent upon the exposure of these devices and products to specific physical variables, such as light, voltage, current, certain chemicals, air pressure, noise, and humidity. In particular, these specific physical variables trigger chemical reactions in these products. These chemical reactions describe physical conditions, such as the spoilage of perishable products, such as foodstuffs, and the expiration of batteries. These chemical reactions are often measured or monitored by natural laws, such as Arrhenius's Law. The actual rate and state of particular chemical reactions depends upon the exposure of these products to specific physical variables. Thus, if users knew the actual time of exposure of particular products specific variables, they would know exactly when certain products will spoil or expire. Users would then know exactly when to discard or recharge certain products, which would allow them to extend or to effectively utilize the useful life of these products. Users could also use this information to record elapsed real time and product shelf life of certain products.
The life and operation of electrical and electronic products, such as integrated circuitry, computer clocks, or batteries used in portable computers and cellular phones, are often dependent upon their exposure to specific physical variables. In particular, integrated circuits typically consist of devices with temperature dependent operating characteristics. For instance, bipolar transistors and diodes have currents with exponential temperature dependence; resistors of various types have various temperature dependencies, which may be either positive or negative; polysilicon capacitors have positive dependencies; field effect transistor threshold voltages have a negative dependency; and crystals for oscillator control may have resonant frequencies with quadratic maxima as a function of temperature. In fact, recognizing the existence of these relationships, many integrated circuit designs already incorporate forms of temperature compensation. For instance, designers often incorporate a temperature sensor plus a responsive heater as part of an integrated circuit package to maintain the temperature of the integrated circuit at a fixed level above ambient. Alternatively, if only certain characteristics need to be temperature compensated, then designers use special circuits, such as a bandgap generator to provide a reference voltage with only a roughly .+-.40 parts per million (ppm) variation per degree Celsius. Similarly, designers use a crystal resonance to control the oscillation frequency of an oscillator, even though the oscillation frequency may vary with temperature.
Similarly, the life and operation of timers or clocks that record exposure-related information is inherently dependent upon their exposure to specific physical variables, such as temperature, because they are ultimately dependent upon these relationships as well. In particular, the temperature dependence of the resonant frequency of the crystal of commonly used clock/calendars may be problematic. The commonly used tuning fork quartz crystal with nominal resonant frequency at 32,768 Hz (2.sup.15 Hz) actually has a parabolic frequency-temperature dependence of: EQU f-f.sub.0 =-K(T-T.sub.0).sup.2
where the maximum resonant frequency, f.sub.0, is close to 32,768, the temperature of maximum resonant frequency, T.sub.0, is close to 25.degree. C., and K is a positive constant. With the maximum resonance frequency occurring at 25.degree. C., the resonant frequency at 0.degree. or 50.degree. C. will be roughly 20 parts per million lower than the nominal maximum of 32,768 Hz. This amounts to the clock running slow and losing several minutes per year. Even in applications where the ambient temperature is well regulated or predictable with the use of specified crystal, such as desktop computers in temperature controlled offices or digital watches on a temperature controlled wrist, these clocks still lose 10-12 minutes per year. In other applications, the loss may be much greater, such as when portable computers may be left in car trunks and encounter very high and very low temperatures in unpredictable cycles. This leads to intolerably poor timekeeping with clocks that use just a crystal for control. This is important, because many electrical and electronic products, such as personal computers, include a clock/calendar that keeps track of the time of day, month, and year in order to time stamp files accurately, insert dates into documents like letters, etc. These clock/calendars are often programmable for setting or changing the date or time of day. Designers typically implement clock/calendars into specific electronic hardware with a dedicated crystal oscillator to provide accuracy and with a battery backup power supply to insure preservation of timekeeping data during an interruption of the primary power supply. This is especially important with personal computers, which are frequently powered down. Likewise, digital watches include a clock/calendar based on a dedicated crystal oscillator and a battery power supply.
Likewise, battery self-discharge and leakage follows an approximately Arrhenius Law independent of the state of charge.
The life and freshness of foodstuffs, such as fruits, vegetables, diary products, and meats, as well as drugs and enzymes, is dependent upon their exposure to specific physical variables, such as temperature as well. `Spoilage` is essentially a chemical reaction.
Unfortunately, despite the importance of this information, existing systems and methods have not been able to overcome the memory requirements associated with recording large amounts of time-sensitive data, which can be overwhelming. Moreover, existing systems and methods are not easily portable. As a result, this information is not generally available to users of many of the chemical, biological, and electrical and electronic products discussed above.